The functioning of the heart and the opening and closing of heart valves occur primarily as a result of pressure differences. For example, the opening and closing of the mitral valve between the left atrium and the left ventricle occurs as a result of the pressure differences between the left atrium and the left ventricle. During ventricular diastole (ventricular filling), when ventricles are relaxed, the venous return of blood from the pulmonary veins into the left atrium causes the pressure in the atrium to exceed that in the ventricle. As a result, the mitral valve opens, allowing blood to enter the ventricle. As the ventricle contracts during ventricular systole (ventricular emptying), the intraventricular pressure rises above the pressure in the atrium and pushes the mitral valve shut. Blood then is pumped from the ventricles to the arteries.
The heart has four valves to ensure that blood does not flow in the wrong direction during the cardiac cycle; that is, to ensure that the blood does not back flow from the ventricles into the corresponding atria, or back flow from the arteries into the corresponding ventricles. The valve between the left atrium and the left ventricle is the mitral valve. The valve between the right atrium and the right ventricle is the tricuspid valve. The pulmonary valve is at the opening of the pulmonary artery. The aortic valve is at the opening of the aorta.
Blood flowing back from the left ventricle into the left atrium, or systolic dysfunction of the left ventricle and valve disease, as mentioned in the background, may cause high atrial pressure and reduce the flow of blood into the left atrium from the lungs. As blood backs up into the pulmonary system, fluid leaks into the lungs and causes pulmonary edema. Blood volume going to the atrium reduces volume of blood going forward into the aorta causing low cardiac output. Excess blood in the atrium over-fills the ventricle during each cardiac cycle and causes volume overload in the left ventricle.
Heart failure with such symptoms is a common and potentially lethal condition affecting humans, with sub-optimal clinical outcomes often resulting in symptoms, morbidity and/or mortality, despite maximal medical treatment.
Congestive heart failure (CHF) is a condition affecting millions of people worldwide. CHF results from a weakening or stiffening of the heart muscle that commonly is caused by myocardial ischemia (due to, e.g., myocardial infarction) or cardiomyopathy (e.g., myocarditis, amyloidosis). CHF causes a reduced cardiac output and inadequate blood to meet the needs of body tissues.
Treatments for CHF include: (1) pharmacological treatments, (2) assisting systems, and (3) surgical treatments. Pharmacological treatments, e.g., with diuretics, are used to reduce the workload of a heart by reducing the blood volume and preload. While pharmacological treatments improve quality of life, they have little effect on survival. Assisting devices, e.g., mechanical pumps, are used to reduce the load on the heart by performing all or part of the pumping function normally done by the heart. However, in a chronic ischemic heart, a high-rate pacing may lead to increased diastolic pressures, calcium overload, and damage to the muscle fibers. There are at least three surgical procedures for treating a heart failure: (1) heart transplant, (2) dynamic cardiomyoplasty, and (3) the Batista partial left ventriculectomy. These surgical treatments are invasive and have many limitations.
CHF is generally classified into systolic heart failures (SHF) or diastolic heart failures (DHF). In a SHF, the pumping action of a heart is reduced or weakened. A normal ejection fraction (EF), which is a function of the volume of blood ejected out of the left ventricle (stroke volume) divided by the maximum volume remaining in the left ventricle at the end of a diastole or relaxation phase, is greater than 50%. In a SHF, the EF is reduced to less than 50%. A patient with a SHF may have an enlarged left ventricle because of cardiac remodeling developed to maintain an adequate stroke-volume. This pathophysiological phenomenon is often associated with increased atrial pressure and left ventricular filling pressure.
DHF is a heart failure without any major valve disease even though the systolic function of the left ventricle is preserved. Generally, DHF is a failure of the ventricle to adequately relax and expand, resulting in a decrease in the stroke volume of the heart. In particular, “diastolic heart failure” refers to the clinical syndrome of heart failure occurring in the context of preserved left ventricular systolic function (ejection fraction) and in the absence of major valvular disease. This condition is characterized by a stiff left ventricle with decreased compliance and impaired relaxation, which leads to increased end-diastolic pressure. Approximately one third of patients with heart failure have diastolic heart failure and there are very few, if any, proven effective treatments. Presently, there are very few treatment options for patients suffering from DHF. DHF afflicts between 30% and 70% of patients with CHF.
There are several known techniques used to treat symptoms of DHF. Without attempting to characterize the following references, for example, U.S. Pat. No. 8,091,556 by Keren et al. discloses the use of an interatrial pressure relief shunt with a valve and a tissue affixation element at each end of the shunt; and United States Patent Application Publication No. 20050165344 by Dobak discloses a pressure relief system with an interatrial septal conduit with an emboli barrier or trap mechanism to prevent cryptogenic stroke due to thrombi or emboli crossing the conduit into the left side circulation. Dobak also discloses a conduit with a one-way valve that directs the blood flow from the left atrium to the right atrium.
The constantly evolving nature of heart failures represents a significant challenge for developing an efficient treatment. Therefore, there is a need for novel and adaptable methods and devices for treating DHF, for example, by creating a pressure relief shunt which can be retrieved, repositioned, adjusted, expanded, contracted, occluded, sealed and/or otherwise altered as required to treat a patient.
In the past, strategies have been described for the relief of high pressure in the right atrium, such as the creation of hole(s) in the native or surgically created septum between the left and right atria. These have been designed for the rare conditions of pulmonary hypertension or cavopulmonary connections for certain complex congenital heart diseases. Accordingly, there still exists a need for devices and methods to treat heart failure, particularly diastolic and/or systolic failure of the left ventricle and its consequences.